1. Field of the Invention
The present invention relates to an SLR (single lens reflex) digital still camera.
2. Description of the Related Art
In a known SLR digital still camera, a stationary half mirror is provided in a photographing light path to allow object-carrying light, transmitted through a photographing lens, to be partly incident on a finder optical system and partly incident on a CCD. The stationary half mirror simplifies the structure of the SLR digital still camera but inevitably causes a loss of light quantity thereby. Consequently, if a photographing lens which collects a large quantity of light is used, inherent advantages thereof cannot be satisfactorily obtained upon photographing.
It is an object of the present invention to provide a SLR digital still camera using a half mirror, in which loss of light upon photographing can be reduced.
To achieve the object mentioned above, according to an aspect of the present invention, there is provided an SLR digital still camera including: a half mirror which allows object-carrying light, transmitted through a photographing lens, to be partly incident on a finder optical system and partly incident on an image pick-up device; a mirror driving device for driving the half mirror between a viewing position and a photographing position; wherein the half mirror is located in a photographing light path to allow object-carrying light, transmitted through the photographing lens, to be incident on a finder optical system when in the viewing position; and the half mirror is retracted from the photographing light path to allow the object-carrying light to be incident on the image pick-up device when in the photographing position; a controller for calculating a displacement from a provisional focus position, based on an electrical signal obtained by a photo-electric conversion of the object-carrying light made incident on the image pick-up device through the half mirror when the half mirror is in the viewing position, to obtain a focusing position in which the photographing lens is focused on an object to be photographed when the half mirror is retracted from the photographing light path; a memory for storing the focus position; and a drive mechanism that moves one of the photographing lens and the image pick-up device in accordance with the focus position stored in the memory when the half mirror is moved to the photographing position upon a photographing operation, so that an in-focus image of the photographing lens is formed on the image pick-up device.
Preferably, the memory stores the focus position of the photographing lens when a shutter button is depressed by a half-step, and the photographing lens is moved to the focus position by the drive mechanism when the shutter button is fully depressed.
Preferably, a program including a step to move the photographing lens to a provisional focus position is stored in the memory in which the object contrast detected by the image pick-up device attains an optimum level when the shutter button is depressed by a half-step, and a step that moves the photographing lens to the focus position from the provisional focus position.
Preferably, a program including a step to move the image pick-up device to a provisional focus position is stored in the memory in which the object contrast detected by the image pick-up device attains an optimum level when the shutter button is depressed by a half-step, and a step that moves the image pick-up device to the focus position from the provisional focus position.
Preferably, an object brightness is detected in accordance with an electric signal which is obtained by a photo-electric conversion of object-carrying light made incident on the image pick-up device through the half mirror in the viewing position.
Preferably, an object brightness is detected in accordance with an electric signal which is obtained by a photo-electric conversion of object-carrying light made incident on the image pick-up device in the viewing position, where the object-carrying light is not transmitted through the half mirror.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 10-272320 (filed on Sep. 25, 1998) which is expressly incorporated herein by reference in its entirety.